There is known a delamination container which is composed of a laminate of at least two layers including an outer layer and an inner layer capable of being delaminated from the outer layer to perform volume reduction deformation and in which an outside air introduction hole for introducing the outside air into between the outer layer and the inner layer is formed in the outer layer (see, for example, PTL 1). According to this container, when the outside air is introduced into between the outer layer and the inner layer from the outside air introduction hole with a decrease in the contents preserved within the inner layer, the inner layer is delaminated from the outer layer, whereby only the inner layer is subjected to volume reduction deformation without causing deformation of the outer layer. As a result, it is possible to prevent the contents from oxidation without causing direct contact of the contents with the air until the contents are emptied completely.
In such a delamination container, a polyolefin, such as polyethylene and polypropylene, is used as a resin for outer layer, and nylon, an ethylene-vinyl alcohol copolymer, or the like is used as a resin for inner layer. In PTL 1, a nylon-made resin which does not substantially have compatibility with a low-density polyethylene-made resin is described as the resin for inner layer.
As for the delamination container, improvements are being advanced every year. For that reason, though further investigations are also demanded with respect to the resin for inner layer to be used therefor, those are not sufficient.
For example, in PTL 2, flexible synthetic resins having a flexural modulus of elasticity of 10,000 kg/cm2 or less are described, and specifically, a nylon 6 copolymer having a flexural modulus of elasticity of 650 kg/cm2 is described. In the delamination container described in PTL 2, from the viewpoint of preventing interlaminar delamination of the seal part formed in the container bottom from occurring, a nerve resin material having a flexural modulus of elasticity of more than 10,000 kg/cm2 could not be used.
On the other hand, in the delamination container described in PTL 1, the interlaminar delamination of the seal part formed in the container bottom is positively utilized as the outside air introduction hole for introducing the outside air into between the outer layer and the inner layer. For that reason, even among materials which could not be used as the resin for inner layer at that time when PTL 2 was described, some of them have become usable as a result of a structural improvement of the container. Meanwhile, in PTL 1, the nylon-made resin is merely generally described as a suitable material, and it is not specifically disclosed on what kind of nylon-made resin is suitable.